The three-dimensional structure of the proteasome from the archaebacterium Thermoplasma acidophilum has been elucidated by x-ray crystallographic analysis by means of isomorphous replacement and cyclic averaging. The atomic model was built and refined to a crystallographic R factor of 22.1 percent. The 673-kilodalton protease complex consists of 14 copies of two different subunits, alpha and beta, forming a barrel-shaped structure of four stacked rings. The two inner rings consist of seven beta subunits each, and the two outer rings consist of seven alpha subunits each. A narrow channel controls access to the three inner compartments. The alpha 7 beta 7 beta 7 alpha 7 subunit assembly has 72-point group symmetry. The structures of the alpha and beta subunits are similar, consisting of a core of two antiparallel beta sheets that is flanked by alpha helices on both sides. The binding of a peptide aldehyde inhibitor marks the active site in the central cavity at the amino termini of the beta subunits and suggests a novel proteolytic mechanism.
PDB ID: 1PMADownload
MMDB ID: 50848
PDB Deposition Date: 1994/12/19
Updated in MMDB: 2007/10
Experimental Method:
x-ray diffraction
Resolution: 3.4  Å
Source Organism:
Similar Structures:
Biological Unit for 1PMA: 28-meric; determined by author and by software (PISA)
Molecular Components in 1PMA
Label Count Molecule
Proteins (28 molecules)
Proteasome(Gene symbol: TA_RS06650)
Molecule annotation
Proteasome(Gene symbol: TA_RS03155)
Molecule annotation
* Click molecule labels to explore molecular sequence information.

Citing MMDB